Most questions closed as duplicates are...duplicates
Why are questions able to be marked as duplicate without some more in depth review?
To be closed as 'duplicate' a question must be reviewed by no less than 5 separate community members (or more rarely, a single moderator or user that's earned a gold badge in one of the question's tags). This process ensures that either highly experienced users or the majority of those tasked with reviewing potential duplicates agree it should be closed. Because of this, the bulk of questions that get closed as duplicate, are in fact, duplicate questions.
For those questions closed as duplicate that indeed are not, the most common cause is insufficient information to distinguish the question from the proposed duplicate. This appears to be the case with your question, which in its current form gives no clear evidence that it's different from the duplicate question. Which leads us to your second (and quite relevant) question...
Why is there no way to appeal or question the decision as the asker?
There is! The FAQ for Duplicate Questions explains what to do if your question is closed as a duplicate, but you disagree:
If you're the author, edit your question to explain how it differs....Questions edited within five days of closure will be added to the reopen queue.
The edit shouldn't merely express disagreement with the closure, but rather explain in detail why your question is not a duplicate. Be detailed and specific so that the reviewers deciding whether your question should be re-opened have the information they need to make a proper decision. Again, it will take 5 reopen votes to get your question opened.
How to avoid getting your question closed as a duplicate in the first place
Knowing that questions can (and if indeed duplicate, should!) be closed as duplicate, it's important to search the site for the answer to your question before posting. To this end, the site assists by displaying possible duplicates based on the content of your question draft. Not only should you review these potential duplicates, but if you find some that are similar but not the same (and thus could tempt question closure), take proactive action by mentioning in your post that you reviewed said question then explain why that question is not a dup.